JPS5932832A - Temperature measuring method - Google Patents

Abstract

PURPOSE:To make it possible to perform accurate measurement of the temperature of a body to be measured, with the emissivity of the body to be measured being obtained by radiation thermometers, by obtaining the total emissivity of the body to be measured and the temperature of each measuring point of the body to be measured at a specified time by expressions. CONSTITUTION:Each measuring point of a body to be measured, which is moved at a constant speed, passes the interval between a first measuring position and a second measuring position, which are separated each other. The time DELTAt required for passing is determined in advance. Radiation thermometers are arranged at the first measuring position and the second measuring positions. The radiation thermometers measure the amount of radiation S(t) radiated from the measuring points of the body to be measured at the time (t) when each measuring point passes the each measuring position (the amount of radiation S1 radiated from the first measuring position and the amount of radiation S2 radiated from the second measuring position). The total emissivity epsilon of the body to be measured is obtained by the expression I . A temperature T(t) of each measuring point of the body to be measurd at the time (t) is obtained by the expression II. Since the emissivity and the temperature are computed in this way, the radiation thermometers (radiometers) are not rquired to be arranged in the vicinity of the body to be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature measuring method using a radiation thermometer, and particularly to a temperature measuring method suitable for use in hot rolling lines and the like.

Generally, the radiometer E from the object to be measured that enters the radiation thermometer is approximated by the following formula.

E=εKTn Here, ε is the emissivity of the object to be measured, K is a constant, n is the radiation constant C2, the wavelength λ, and the temperature T of the object to be measured, so that n=C
It is expressed as 2/λ·T and is usually called the n value. In other words, as shown in the above equation, a radiation thermometer alone measures the amount of radiation from an object to be measured, and since there is an uncertain parameter of emissivity ε that differs depending on the object to be measured, Accurate measurement is not possible, and in order to solve this problem, methods have been proposed in the past, such as using a gold-plated cavity or the like to measure in a state close to thermal equilibrium.

However, in methods using gold-plated cavities or other blackened cavities, it has been advantageous to measure the cavities as close to the object to be measured as possible and close to a state of thermal equilibrium. That is, there is a problem in that the measuring device must be placed close to the object to be measured, and it is difficult to normally install it at the measuring position.

SUMMARY OF THE INVENTION An object of the present invention is to provide a temperature measurement method that enables accurate measurement of the temperature of an object to be measured while determining the emissivity of the object using a radiation thermometer.

In order to achieve the above object, the temperature measurement method according to the present invention provides a first measurement position and a second measurement position in which each measurement point of a measurement object moving at a constant speed is spaced apart from each other in the direction of the moving force. By predetermining the time Δt required for passing between the positions, each radiation thermometer placed at the first measurement position and the second measurement position determines the time at which each measurement point of the object passes through each measurement position. The amount of radiation S(t
) (Radiation amount S emitted by each measured point at the first measurement position, and radiation amount S2 emitted at the second measurement position)
Measure the total emissivity ε of the object to be measured, (where c is the specific heat of the object to be measured, w is the weight per unit surface area of the object to be measured, σ is the Stefan-Poltzmann constant, and θ is the The amount of heat that the object loses due to heat conduction between the first measurement position and the second measurement position), and the temperature T(t) at each measurement point of the wave measurement object at time t is determined by T(t) = ε・S( ).

The present invention will be explained in more detail below.

FIG. 1 is a measurement system diagram showing an example of a measuring device used in implementing the present invention. An object to be measured 1 having a high temperature compared to the ambient temperature is being moved at a constant speed by a conveying roller 2. A first radiation thermometer 3 and a second radiation thermometer 4 are installed at a first measurement position and a second measurement position, which are spaced apart from each other in the moving direction of the object to be measured 1, respectively. Each radiation thermometer 3, 4 measures the amount of radiation emitted by the object to be measured passing through each measurement position using a sighting tube 5 for limiting the field of view.
Measure through. The radiation amounts measured by the radiation thermometers 3 and 4 are sequentially transmitted to the signal processor 6, and the signal processor 6 calculates the temperature of the object to be measured according to a temperature calculation formula described later. In the figure, 7 is a CRT display, which is capable of displaying the temperature distribution in the moving direction of the object to be measured 1 calculated by the signal processor 6. Further, reference numeral 8 denotes a measured object detection switch, which detects the approach of the measured object 1 and enables the signal processor 6 to start operating.

Next, an inventive temperature calculation formula obtained using the amount of heat lost in a certain period of time by an object to be measured whose temperature is higher than the ambient temperature will be explained.

First, radiation and thermal conduction (
The heat Q5 lost from the surface due to convection (only convection is considered here) is. However, t1 is the time when a certain measured point of the measured object passes the first measurement position, and t2 is the time when the measured point of the measured object passes the second measurement position. In addition, F(T) in the above formula (1) is F
(T)=2F1(T)+2F2(T)...(2), where F1(T) is due to radiation and F2(T) is due to thermal conduction.The unit is the measured point where the measured object is at temperature T. It is the amount of heat lost over time, and in equation (2), it is doubled to take into account the front and back surfaces of the object to be measured. Here, F
1(T) is F1(T)=ε・σ・{T(t)4−T4a}...(3
). However, ε is the total emissivity of the object to be measured, σ is the Stefan-Boltzmann constant, and σ=5.67X10−
8 [W·m-2·K-4]. Furthermore, T(t) is the temperature at a point to be measured at the object to be measured at time t, and Ta is the ambient temperature. Also, the convection term F2(T) is F2(T
)=α・{T(t)−Ta}β...(4).

However, α is the heat transfer coefficient and β is a constant. Here, when the object to be measured is in a high temperature state, F2(T) is F1(
F2(T)=θ/2・Δt using a constant value of 0 within a relatively short time.
...(5). Note that θ is
Using equation (4), the heat transfer coefficient α is calculated using literature values, and the ambient temperature Ta is calculated from the average value in the range of fluctuations of the room temperature and the temperature T of the object to be measured. It is also necessary to compare the value with other contact surface thermometers and confirm the value experimentally. However, each measured point of the measured object is
The time required to pass between the measurement position and the second measurement position was set as Δt=t2−t1.

Note that since the object to be measured is moving at a constant speed, Δt is predetermined based on its moving speed and the distance between each measurement position.

Using the above equations (3) and (5), QS is expressed by the following equation.

Furthermore, if the temperature of the object to be measured is very high relative to the ambient temperature and T(t)>>Ta, it can be approximated by the following equation (6).

However, at times t1 and t2, the first measurement position and the second measurement position are
Temperatures T(t1) and T(t2)% of the measured point where the measured object passes through the measuring position are respectively set as T1 and T2.

Next, inside the measured point of the measured object, at time t
The amount of heat ΔQ lost between time 1 and time t2 is ΔQ=c・w・
(T1-T2)...(8). However, c is the specific heat of the object to be measured, and w is the weight per unit surface of the object to be measured. In the above equation (8), it is assumed that the temperature change of the object to be measured is small, and the specific heat c is a constant.

Furthermore, it was assumed that the inside of the object to be measured had a sufficiently small thickness or had reached a sufficiently steady state, and that the temperature change (T1-T2) in the thickness direction did not change.

From the heat balance regarding the object to be measured, QS=ΔQ, and therefore, using equations (7) and (8) above, the following relational expression can be obtained.

Here, if a total radiation type is used as the radiation thermometer,
Radiation thermometer indication, that is, radiation amount S(t) at time t
The following relationship holds between T(t) and the temperature T(t) of the measured object at the same time t. Using the above equation (10), the above (
Equation 9) can be transformed as shown in the following equation.

Therefore, by solving the above equation (11), the total radiation ε of the object to be measured can be determined as follows. Next, the above (11)
By substituting the above-mentioned total emissivity ε into the following equation, which is a modified version of the equation, it becomes possible to obtain the temperature T(t) at time t of each measured point of the measurement object, and therefore the temperatures T1 and T2.

The procedure for measuring the temperature distribution in the moving direction of the object to be measured using the above temperature calculation formula is as follows.

First, for each measured point of the measured object, each radioactivity S1, S2 determined by the first radiation thermometer and the second radiation thermometer
are sequentially transmitted to the aforementioned signal processor 6 and stored therein. Next, a pair of radiation amounts S corresponding to each measured point of the measured object
1 and S2 are selected sequentially, and as mentioned above, the temperature T is sequentially determined using a predetermined time Δt, specific heat c of the object to be measured, weight w, ambient temperature Ta, and amount of heat lost due to convection θ.
1 (as well as T2), and the temperature distribution in the moving direction of the object to be measured is determined. In the present invention, the emissivity and temperature of the measured object are calculated using the amount of radiation from the measured object, that is, the amount of heat that the measured object loses per unit time, so in particular a radiation thermometer (radiometer) is used. There is no need to place it close to the object to be measured.

In addition, to give an example of the temperature change of the object to be measured, a thickness of 1 m
m, a rust plate with an emissivity of 0.5 and a temperature of 1,000°C is 1
After seconds the temperature drops by about 30°C. Also, temperatures T1 and T2
There is no calculation limit to the temperature sa, but its upper limit is determined by the range within which physical property values such as specific heat c and total emissivity ε of the object to be measured do not change, and its lower limit is determined by the resolution of the radiation thermometer and Defined by accuracy. Therefore, the installation position of each radiation thermometer should be set at a temperature of 1' to 5()°C while the object to be measured passes through each radiation thermometer. It is preferable to maintain an interval that allows the temperature to change by approximately 5° C. to 50° C. during the change.

In addition, in order to measure the same measurement point of the object to be measured, a second
For the measured radiation amount S2 of the radiation thermometer, it is necessary to use a measured value delayed by a time Δ1 with respect to the measured radiation amount S1 of the first radiation thermometer.

Further, the present invention is effective when the temperature of the object to be measured is higher than the ambient temperature, the temperature change is small, and the thickness of the object to be measured is relatively small.

As described above, in the temperature measurement method according to the present invention, each measured point of a measured object moving at a constant speed is located between a first measurement position and a second measurement position which are spaced apart from each other in the direction of movement. The time Δt required for passing through is predetermined, and the radiation emitted by each measurement point of the object to be measured at the time t of passing through each measurement position by each radiation thermometer placed at the first measurement position and the second measurement position, respectively. Measuring the amount S(t) (the amount of radiation S1 emitted by each measured point at the first measurement position and the amount S2 of radiation emitted at the second measurement position),
The total emissivity ε of the measured object is expressed as, (where c is the specific heat of the measured object, w is the weight per unit surface area of the measured object, σ is the Stefan-Poltzmann constant, and θ is the The amount of heat lost due to heat conduction between the measurement position and the second measurement position), and the temperature T(1) of each line measurement point of the object to be measured at time t is calculated as: T(t)=ε-1/4・S (t) Therefore, it becomes possible to accurately measure the temperature of the object to be measured while determining the emissivity of the object to be measured using the radiation thermometer.

[Brief explanation of the drawing]

FIG. 1 is a measurement system diagram showing an example of a measuring device used in implementing the present invention. 1... Object to be measured, 3... First radiation thermometer, 4...
Second radiation thermometer.

Claims (1)

[Claims] (1) Determine in advance the time Δt required for each measured point of the measured object moving at a constant speed to pass between the first measurement position and the second measurement position that are separated from each other in the direction of the moving force. , the amount of radiation S(
t) (Radiation amount S1 emitted by each measured point at the first measurement position and radiation amount S2 emitted at the second measurement position
), and the total emissivity ε of the object to be measured is determined by (where c is the specific heat of the object to be measured, w is the weight per unit surface area of the object to be measured, σ is the Stefan-Polzmann constant, and θ is the object to be measured. The amount of heat that the object loses due to thermal conduction between the first measurement position and the second measurement position) is calculated, and the temperature T(t) of each measurement point of the object at time t is determined as 4.Sft) Temperature measurement method.